1. Field of the Invention
The present invention relates to a square shaped battery, and specifically to a square shaped battery including an electrode plate group formed by rolling a belt-like positive electrode plate, a belt-like negative electrode plate, and a belt-like separator.
2. Description of the Related Art
In the case where a battery case is made of resin, electrode plates are laminated, and leads connected to end portions of respective electrode plates are gathered.
In the case where a battery case is made of metal, a portion of a belt-like positive electrode plate and a sealing plate are both welded to a lead where the lead is connected between the portion of the belt-like positive electrode plate and the sealing plate, and a negative electrode plate is connected to the metal battery case through a lead or contacted directly with the metal battery for collecting electric power.
A conventional square shaped battery 900 is now described with reference to FIG. 9.
The square shaped battery 900 includes positive electrode plates 1 and negative electrode plates 2. Each of the positive electrode plates 1 is formed of foamed nickel so as to have an unfilled portion having a 5 mm width at an end thereof. The unfilled portion is filled with a positive electrode material mainly composed of nickel hydroxide. A nickel lead is attached to the portion filled with the positive electrode material. The capacity of the positive electrode plate 1 is about 1 Ah (Ampere hour). Each negative electrode plate 2 is formed by punched metal which is coated with a negative electrode material mainly composed of hydrogen occlusion alloy so as to leave an uncoated portion having a 5 mm width at an end thereof. The capacity of the negative electrode plate 2 is about 1.25 Ah.
The positive electrode plates 1 are each covered with a sack-like separator 3 formed of nonwoven polypropylene fabric. Seven positive electrode plates 1 and eight negative electrode plates 2 are alternately superposed thus forming an electrode plate group. Nickel leads 4 are provided to the electrode plates 1 and 2. The nickel leads 4 are gathered at an upper end of the electrode plate group, and connected to external positive and negative terminals by resistance-welding. A resin case is used as a battery case for containing the square shaped battery 900. The battery case containing the square shaped battery 900 is filled with electrolyte mainly composed of potassium hydroxide, and then, the square shaped battery 900 is charged and discharged at 0.1 C (Capacity) for activation. The capacity of the square shaped battery 900 is about 7 Ah.
Another conventional square shaped battery 1000 is now described with reference to FIG. 10.
The square shaped battery 1000 includes a belt-like positive electrode plate 5 and a belt-like negative electrode plate 6. The positive electrode plate 5 is formed of foamed nickel so as to have an unfilled portion of 5 mmxc3x975 mm at an end thereof. The unfilled portion is filled with a positive electrode material mainly composed of nickel hydroxide. A nickel lead is attached to the portion filled with the positive electrode material. The capacity of the positive electrode plate 5 is about 7 Ah. The negative electrode plate 6 is formed by punched metal which is coated with a negative electrode material mainly composed of hydrogen occlusion alloy so as to leave an uncoated portion of 5 mmxc3x975 mm at an end thereof. The capacity of the negative electrode plate 6 is about 10 Ah.
A separator 7 made of nonwoven polypropylene fabric is interposed between the positive electrode plate 5 and the negative electrode plate 6, and a laminate of the positive electrode plate 5, the separator 7, and the negative electrode plate 6 is rolled to form an electrode plate group. For the purpose of connection with an external terminal (i.e., for the purpose of collecting electric power), a nickel lead 8 provided to the positive electrode plate 5 is welded to a sealing plate, and a negative electrode is connected to a battery case. The battery case is made of a metal. The battery case containing the square shaped battery 1000 is filled with electrolyte mainly composed of potassium hydroxide, and then, the square shaped battery 1000 is charged and discharged at 0.1 C for activation. The capacity of the square shaped battery 1000 is about 7 Ah.
In the case of a high power battery for use in hybrid energy vehicles (HEVs), etc., the electrochemical reaction resistance is reduced by increasing the area of the electrodes, whereby the power of the battery is increased. However, in the case where electric power is not sufficiently collected from an electrode plate group, desired high power cannot be obtained even if the electrochemical reaction resistance is reduced. Furthermore, when plate-shape electrodes are used, a large number of electrodes are required, and accordingly, the number of production steps increase.
According to one embodiment of the present invention, a square shaped battery includes: an electrode plate group including a belt-like positive electrode plate, a belt-like negative electrode plate, and a belt-like separator, the belt-like positive electrode plate, the belt-like negative electrode plate, and the belt-like separator being laminated and rolled up to form the electrode plate group; and a pair of power collectors disposed on sides of the electrode plate group for collecting electric power from the electrode plate group.
In one embodiment of the present invention, the pair of power collectors are welded to the sides of the electrode plate group.
In another embodiment of the present invention, a welding interval of each of the power collectors is narrower in an upper portion than in a lower portion.
In still another embodiment of the present invention, the pair of the power collectors have protrusions for obtaining a sufficient welding area through which the pair of the power collectors are welded to the electrode plate group.
In still another embodiment of the present invention, each of the protrusions has a hollow portion.
In still another embodiment of the present invention, each of the pair of the power collectors has a central portion in which a protrusion is not provided, and the central portion is pressed against the electrode plate group with the power collector being welded to the electrode plate group.
In still another embodiment of the present invention, the pair of power collectors are disposed on both sides of the electrode plate group such that a width direction of the electrode plate group is substantially perpendicular to faces of the pair of power collectors.
In still another embodiment of the present invention, one of the pair of power collectors collects electric power from the electrode plate group in a direction different from that of the other of the pair of power collectors.
In still another embodiment of the present invention, each of the pair of power collectors has a xe2x80x9cUxe2x80x9d-shape which binds the electrode plate group so as to suppress expansion of the sides of the electrode plate group.
According to one aspect of the present invention, belt-like electrode plates are rolled up to form an electrode plate group, and electric power is collected from the entire side faces of the rolled electrode plate group, whereby the resistance in power collectors can be reduced. With such a structure, increased electric power due to the increase in electrode plate area can be efficiently collected. Furthermore, the number of steps for forming the electrode plate group can be reduced.
According to another aspect of the present invention, the facing area of electrode plates (i.e., the surface area between adjacent plates) can be increased while reducing the number of electrode plates.
Thus, the invention described herein makes possible the advantages of (1) providing a high-power square shaped battery, (2) providing a square shaped battery in which electric power can be sufficiently collected, and (3) providing a square shaped battery in which an electrochemical reaction resistance can be reduced.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.